Double metal cyanide (DMC) complexes are well-known catalysts for epoxide polymerization. These active catalysts give polyether polyols that have low unsaturation compared with similar polyols made using basic (KOH) catalysis. The catalysts can be used to make many polymer products, including polyether, polyester, and polyetherester polyols. The polyols can be used in polyurethane coatings, elastomers, sealants, foams, and adhesives.
DMC catalysts are usually made by reacting aqueous solutions of metal salts and metal cyanide salts to form a precipitate of the DMC compound. A low molecular weight complexing agent, typically an ether or an alcohol, is included in the catalyst preparation. Other known complexing agents include ketones, esters, amides, ureas, and the like. See, for example, U.S. Pat. Nos. 4,477,589, 3,829,505, and 5,158,922. The traditional favorite complexing agent has been glyme (dimethoxyethane), which gives DMC catalysts having activities within the range of about 0.1 to about 0.5 kg PO/g Co/min. at 100 ppm, based on the weight of finished polyether, at 105.degree. C.
Recently, I discovered (see U.S. Pat. No. 5,482,908, "the '908 patent") that the activity of DMC catalysts is greatly enhanced by incorporating, in addition to the organic complexing agent, from about 5 to about 80 wt. % of a polyether having a number average molecular weight greater than about 500. Catalysts that contain both an organic complexing agent (e.g., tert-butyl alcohol) and a polyether polyol can polymerize propylene oxide at rates in excess of 2 kg PO/g Co/min. at 100 ppm catalyst, based on the weight of finished polyether, at 105.degree. C. In contrast, a catalyst containing polyol but no tert-butyl alcohol was inactive, and a catalyst made with only tert-butyl alcohol was less active. Our initial work suggested that polyethers having molecular weights lower than 500 and polyethylene glycols were generally not suitable or gave much less active catalysts.
The ability to make very active DMC catalysts with low molecular weight polyethers would be valuable because low molecular weight polyethers are often cheaper or more readily available than those having molecular weights greater than 500. Ideally, these DMC catalysts would offer the advantages of the catalysts described in the '908 patent. For example, they would give polyether polyols with very low unsaturation, and would be active enough to allow their use at a very low concentrations, preferably at concentrations low enough to overcome any need to remove the catalysts from the polyol.